Use of a pyridazinone derivative

ABSTRACT

A method for the treatment of neurohumoral imbalance caused by alterations of cardiac function to prevent the development of heart failure comprises administering an effective amount of (R)-N-[4-(1,4,5,6-tetrahydro-4-methyl-6-oxo-3-pyridazinyl)phenyl]acetamide to a mammal in need of such treatment.

The intention invention relates to a method for the treatment ofneurohumoral imbalance caused by alterations of cardiac function toprevent the development of heart failure by administering an effectiveamount of(R)-N-[4-(1,4,5,6-tetrahydro-4-methyl-6-oxo-3-pyridazinyl)phenyl]acetamideto a mammal in need of such treatment.

RacemicN-[4-(1,4,5,6-tetrahydro-4-methyl-6-oxo-3-pyridazinyl)phenyl]acetamide(I) has been described earlier as a hypotensive agent (U.S. Pat. No.3,746,712) and as a cardiotonic agent having inotropic activity (U.S.Pat. No. 4,397,854). It has been reported that the inotropic action ofracemicN-[4-(1,4,5,6-tetrahydro-4-methyl-6-oxo-3-pyridazinyl)phenyl]acetamideis based on phosphodiesterase III (PDE III) enzyme inhibition (Ishimorit. et al., Arzneim.-Forsch. (1994) 44(5), 583-8). The compound (I) hasan asymmetric carbon atom and may therefore exist in two stereoisomericforms. The (R)- and (S)- enantiomers of (I) has been earlier describedin Japanese patent application no. (Heisei) JP 3163050. However,biological activity data for the enantiomers has not been described.

At the moment series of inotropic compounds, e.g. milrinone, themechanism of which is based on PDE III inhibition are in clinical trialsfor the treatment of heart failure. These compounds increase thecontractility of the cardiac muscle by increasing the calcium currentinto the cardiac muscle and produce vasodilatation. The contraction incardiac muscle is triggered by the binding of calcium in troponin.However, it is possible that the long-term application of PDE IIIinhibitors leads to calcium overload in the cardiac muscle which cantrigger arrhythmias. Therefore, the main mechanism to increase cardiaccontractility should be a mechanism which does not produce calciumoverload. The enhancement of the turnover of intracellular calciumreleased from sarcoplasmic reticulum and the increase of calciumsensitivity of contractile proteins are such mechanisms which do notinduce calcium overload.

When a patient has harmful alterations in the cardiac function, thecontractility of the cardiac muscle can still be maintained throughneurohumoral activation in the body, which increases the intake ofcalcium in the cardiac muscle. In this situation the calcium overloadcan trigger arrhythmias, and prolonged neurohumoral activation willaccelerate the development of heart failure. Neurohumoral imbalance canbe indicated, for example, by altered renin and noradrenalineconcentrations in a patient's plasma. PDE III inhibitors can not be usedchronically in the treatment of neurohumoral imbalance because theyfurther increase the intake of calcium into the cardiac muscle. However,the use of a calcium sensitizer can sufficiently increase thecontractility already in normal and decreased calcium concentrationswhich would reduce the need of neurohumoral activation and therebyprevent the development of heart failure.

It has been now discovered that the (R)-enantiomer ofN-[4-(1,4,5,6-tetrahydro-4-methyl-6-oxo-3-pyridazinyl)phenyl]acetamidehas a calcium sensitizing effect on troponin and that its main mechanismto increase cardiac contractility is the increase of calcium sensitivityof troponin. This was unexpected since the mechanism of rasemic compound(I) was reported to be PDE III inhibition. Thus, being a calciumsensitizer the (R)-enantiomer ofN-[4-(1,4,5,6-tetrahydro-4-methyl-6-oxo-3-pyridazinyl)phenyl]acetamidehas a utility in the treatment of neurohumoral imbalance caused byalterations of cardiac function to prevent the development of heartfailure.

The present invention relates to a method for the treatment ofneurohumoral imbalance caused by alterations of cardiac function toprevent the development of heart failure by administering orally orparenterally in a solid or liquid dosage form an effective amount of(R)-enantiomer of compound (I) to a patient in need of such treatment.

The pharmaceutically active compound according to this invention isformulated into dosage forms using the principles known in the art. Itis given to a patient as such or in combination with suitablepharmaceutical excipients in the form of tablets, dragees, capsules,suppositories, emulsions, suspensions or solutions. The compositionaccording to the invention contains a therapeutically effective amountof the pharmaceutically active compound of the invention. The contentsof the active compound is in the composition from about 0.5 to 100% perweight.

In the claimed method the compound of the invention may be administeredto man in oral doses ranging from about 0.1 to 500 mg, preferably 0.5 to10 mg, per day. Choosing suitable ingredients for the composition is aroutine for those of ordinary skill in the art. It is evident thatsuitable carriers, solvents, gel forming ingredients, dispersion formingingredients, antioxidants, colours, sweeteners, wetting compounds andother ingredients normally used in this field of technology may be alsoused.

The following example will further illustrate the invention.

EXAMPLE 1 Preparation of(R)-N-[4-(1,4,5,6-tetrahydro-4-methyl-6-oxo-3-pyridazinyl)phenyl]acetamide

(R)-6-(4-aminophenyl)-4,5-dihydro-5-methyl-3(2H)-pyridazinone (30.0 g)and acetonitrile (600 ml) were mixed and the mixture was refluxed untilthe starting material dissolves. Acetic anhydride (30.0 ml) was added tothe refluxing mixture. After 10 min the solution was allowed to cool toroom temperature. The product was filtered, washed with acetonitrile anddried.

Yield 30.8 g, mp 230-232, ¹H-NMR (DMSO-d₆, 400 MHz) 1.06 (d, 3H, J=7.3Hz), 2.06 (s, 3H), 2.22 (d, 1H, J=16.6 Hz), 2.67 (dd, 1H, J=16.6 Hz, 6.8Hz), 3.35 (m, 1H), 7.63 (d, 2H, J=8.8 Hz), 7.72 (d, 2H, J=8.8 Hz), 10.09(s, 1H), 10.88 (s, 1H). [α]_(D) ²⁰=−466° (c=2 mg/ml, DMF).

The usefulness of the compound of the invention is demonstrated by thefollowing experiments. Compound A is(R)-N-[4-(1,4,5,6-tetrahydro-4-methyl-6-oxo-3-pyridazinyl)phenyl]acetamide.

Calcium Sensitizing Effect in Skinned Cardiac Fiber

Left ventricular papillary muscle of the guinea-pig was dissected andrinsed in ice-cold Tyrode solution. Thereafter the papillary muscle wasimmersed into a solution containing (mM): Potassium acetate 74.7, EGTA10, MgSO₄ 5.4, ATP-Na₂ 4, DTE 1, MOPS 20, pH 7.0 (by 1 M KOH).Subsequently, the papillary muscle was sonicated at 10 Watt for 60 secin this ice-cold solution. The distance between ultrasound probe and thepapillary muscle was 10 mm. The fibers (<200 μm in diameter) weredissected from surface of sonicated papillary muscles. Moreover, thesonicated and dissected fibers were kept for 30 min in a “skinning”solution (ice-cold) containing saponin (250 μg/ml) in addition to theother constituents. Continuous magnetic stirring was used during thistreatment.

The fibers which were further dissected (<100 μm in diameter) were thenmounted horizontally with a glue (cellulose acetate in acetone) betweena steel-rod extension of isometric force transducer (AME-801 straingauge, Horten Electronics, Norway) and a glass rod attached to amicro-manipulator. The force transducer was connected to an amplifier.The fibers were kept in the “relaxing” solution containing (mM):imidazole 30, ATP-Na₂ 10, NaN₃ 5, EGTA 5, MgCl₂ 12.5, and 350 Ucreatinkinase. The temperature of the solution was 22° C. and the pH wasset to 6.7 by 1 M KOH. The ionic strength was adjusted with 1 M KCl tocorrespond that of the “activating” solution. The composition of the“activating” solution was the same as that of the “relaxing” solutionexcept that it contained also CaCl₂. The fibers were induced to contractin desired free pCas (−log [Ca²⁺]) which were obtained by properlymixing of the “relaxing” and “activating” solutions. Tension produced bya fiber at pCa 4.8 was taken as maximum response. At the beginning ofthe experiment the fiber was stretched as described above.

TABLE 1 Calcium sensitizing effect in skinned fiber at pCa 5.6 Change inforce % of control Compound A 0.3 μM + 26 ± 6 (n = 7)   3 μM + 109 ± 35(n = 7) Milrinone ineffective

Positive Inotropic Effect in Paced Cardiac Muscle

Four weeks old guinea-pigs weighing about 350 g were used. In theexperiments the right ventricular papillary muscle of the heart wasmounted for measurement of isometric tension in organ bath containingmodified Tyrode solution (37° C.) bubbled with 95% O₂, 5% CO₂. Thecomposition of the modified Tyrode solution was (mM): NaCl 135;MgCl₂.6H₂O 1; KCl 5; CaCl2.2H₂O 2; NaHCO₃ 15; Na₂HPO₄.2H₂O 1; glucose10; pH 7.3-7.4. The volume of the open horizontal chamber was 1 ml andflow rate of the superfusion solution running through the chamber was 5ml/min. Papillary muscle (<1 mm in diameter) was stretched horizontallybetween force-displacement transducer (FT 0.3 and a needle fixed to thebottom of the chamber. An initial stretching tension of 300 mg wasapplied to the muscle which was electrically stimulated (Stimulatormodel SEC 48 F, Grass Instruments) via platinum field electrodes at 1 Hzwith rectangular pulses (duration 4 ms). The stimulation occurred attwice threshold voltage in order to achieve simultaneous activation ofall myocytes in the capillary muscle. A force-displacement transducerwas connected to a polygraph D.C. driver amplifier (model 7 DA, GrassInstruments) and a programmable scanner (model SI 5010, Tetronix). Theamplified signal was digitised with 1 kHz frequency by a programmabledigitizer (model 390 A, Sony Tetronix).

TABLE 2 Positive inotropic effect in guinea-pig papillary muscle EC₅₀/μMCompound A 0.1 Milrinone 2

We claim:
 1. A method for the treatment of neurohumoral imbalance causedby alterations of cardiac function to prevent the development of heartfailure by administering an effective amount of(R)-N-[4-(1,4,5,6-tetrahydro-4-methyl-6-oxo-3-pyridazinyl)phenyl]acetamideto a mammal in need of such treatment.
 2. The method according to claim1, wherein said compound is administered to a human in oral dosesranging from 0.1 to 500 mg per day.
 3. The method according to claim 2,wherein said compound is administered in oral doses ranging from 0.5 to10 mg per day.
 4. A method of increasing calcium sensitivity oftroponin, which method comprises administering an effective amount of(R)-N-[4-(1,4,5,6-tetrahyro-4-methyl-6-oxo-3pyridazinyl)phenyl]acetamideto a mammal.
 5. The method acording to claim 4, wherein said compound isadministered to a human in oral doses ranging from 0.1 to 500 mg perday.
 6. The method according to claim 5, wherein said compound isadministered in oral doses ranging from 0.5 to 10 mg per day.
 7. Amethod of increasing calcium sensitivity of contractile proteins ofcardiac muscle in a mammal, which method comprises administering aneffective amount of (R)-N-[ 4 -( 1,4,5,6 -tetrahydro- 4 -methyl- 6 -oxo-3 -pyridazinyl)phenyl]acetamide to the mammal.
 8. A method for reducingthe need for neurohumoral activation in a patient, which comprisesadministering to the patient an effective amount of (R)-N-[ 4 -( 1,4,5,6-tetrahydro- 4 -methyl- 6 -oxo- 3 -pyridazinyl)phenyl]acetamide.